Interaction of alpinetin with bovine serum albumin: Probing of the mechanism and binding site by spectroscopic methods

The binding interaction between alpinetin and bovine serum albumin (BSA) in physiological buffer solution (pH 7.4) was investigated by fluorescence, UV–vis spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. It was proved from fluorescence spectra that the fluorescence quenching of BSA by alpinetin was probably a result of the formation of BSA–alpinetin complexes, and the binding constant (Ka) were determined according to the modified Stern–Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS), were calculated to be 22.10 kJ mol−1 and 166.04 J mol−1 K−1, respectively, which indicated that the interaction between alpinetin and BSA was driven mainly by hydrophobic interaction. Moreover, the competitive experiments of site markers suggested that the binding site of alpinetin to BSA was located in the region of subdomain IIA (sudlow site I). The binding distance (r) between the donor (BSA) and the acceptor (alpinetin) was 3.32 nm based on the Förster theory of non-radioactive energy transfer. In addition, the results of synchronous fluorescence and FT-IR spectra demonstrated that the microenvironment and the secondary structure of BSA were changed in the presence of alpinetin.